Understanding the Room-Temperature Catalytic Activity of Silver-Containing Mixed Oxides: The Role of Ag 2+ Surface Species

Mixed oxides AgFeO 2 (delafossite) and AgMnO 2 (crednerite) were prepared during hydrothermal synthesis. The catalytic properties were investigated in the low-temperature CO oxidation reaction, depending on the pretreatment temperature in CO + O 2 . Correlations were established between the catalytic activity of mixed oxides, structural features, thermal stability, and silver surface state. Oxide AgMnO 2 was characterized by enhanced reactivity toward CO (below 100 °C) and enhanced oxygen mobility in comparison with AgFeO 2 . In situ XRD and ex situ XPS revealed the relationship between the high catalytic CO oxidation activity of AgMnO 2 and the presence of active oxygen forms related to the Ag 2+ surface species, which were not found on the AgFeO 2 surface. High catalytic activity on the surface of the AgMnO 2 particles is considered to involve a redox cycle with the participation of Ag 2+, Ag 1+, and Ag 0 silver states, while the reduced catalytic activity of AgFeO 2 is caused by the reaction occurring at the interface between the Ag 1+ O x /Ag 0 particles and the delafossite surface, excluding the involvement of Ag 2+ -type species in the redox cycle.